Conventional optical disc storage systems, typically use a single optical sub-assembly, including a light source and a light detector, to read or write the information on an optical disc, such as for example, a compact disc (CD). Therefore, most CDs only have information recorded on a single side. The "flip" side of the CD is generally not used.
In order to access both sides of a double-sided CD, the CD must be flipped over by the user. The problem with such systems is that only one side of recorded information is accessible at any one time, and also the CD is more likely to be damaged due to excessive handling.
FIG. 1 shows the problems associated with delivering a light beam from a single optical subassembly to both sides of an optical disc. In FIG. 1, there is shown an optical storage system of the type that can advantageously use the invention. It should be understood that the optical subassembly 5 generates a single light beam along the path indicated by reference numeral 1. The problem is to selectively direct this light beam along paths 1' and 1" to a first and second recording surface 11 and 12 of the disc 10 snap mounted onto the end of a spindle 21. The spindle 21 and the disc 10 are rotated by a motor 22.
The system further includes a first and a second directing mirror 41, and 42 for directing the light beam parallel to the plane of the disc 10, along either path 1' or path 1".
A first and second reflecting mirror 51 and 52 are attached to the end of actuator arms 61 and 62. The arms 61 and 62 radially position the reflecting mirrors 51 and 52 relative to the recording surfaces 11-12 of the disc 10. The reflecting mirrors 51 and 52 reflect the light beams from path 1' or path 1", perpendicularly to the recording surfaces 11 and 12, respectively.
At the recording surfaces 11 and 12, the light beam is modified and reflected back along its incident path to the optical subassembly 5, where the modified and reflected light beam is decoded and processed.
The embodiments of the invention described herein are envisioned for use with magneto-optical disc technology. In magneto-optical disc technology the well known Hall effect is used to modify the light beam at the recording surface. Read-only discs use variations in the surface topology of the recording surface to modify the light beam. However, the mechanism disclosed is also applicable to other optical disc technologies, fixed or removable, single or multi-disk, and including write once, read only, and audio and video CD.
The problems which exist in the system occur at the point generally indicated by reference numeral X. Means need to be provided which can rapidly, inexpensively, and selectively direct the light beam from path 1 to either path 1' or path 1".
Prior art system have used galvo-galvanic mirrors at point X. "Galvo-mirrors" are well known in the art. However, galvo-mirrors are relatively expensive and require complex servo control systems to accurately rotate the mirror to the desired angles. Also galvo mirrors may require longer settling times after positioning which induced latency into the system.